The present invention relates to a recording unit structure and a recording device. In further detail, the present invention relates to a thermal recording unit structure and a thermal recording device comprising the unit structure.
With the move of society into the information age furnished with more colorful recorded images supported by a variety of information media such as video cameras, television sets, and computer graphics, demand is rapidly growing for colored hard copies. To meet for the demand, color printers based on various types of recording methods are developed and provided to a variety of fields.
Among the various types of recording methods is included a technique comprising transferring a transfer dye from an ink sheet to an image receiving layer corresponding to the heat applied to the sheet. This method comprises bringing an ink sheet into contact with an image transfer body while applying a predetermined pressure thereto. More specifically, an ink sheet having thereon an ink layer coating containing a certain type of binder resin having dispersed therein a transfer dye at a high concentration is brought into contact with an image transfer body such as a photographic paper having thereon a dye receiving resin which receives the transferred dye while applying pressure thereto, and heat is applied in correspondence to the image information by means of a thermosensitive recording head placed on the ink sheet.
The operation above is then repeated for each of the image signals obtained by separating the initial image signal into the three subtractive primaries, i.e., yellow, magenta, and cyan. In this manner, a full-color image having a continuous gradation can be obtained by a so-called thermal transfer recording method. The thermal transfer color process is now attracting much attention as a promising technique concerning its capability of making the recording system compact, ease in maintenance, and instantaneous recordability, and yet, it is believed capable of producing high quality images well comparable to those of the conventional silver halide photographs.
Referring to the schematic front view shown in FIG. 33, the essential portion of a printer of a thermal transfer type is described below.
A thermal recording head (hereinafter referred to simply as "a thermal head") 61 is faced to a platen roller 63, and an ink sheet 62 comprising a base film 62b having thereon an ink layer 62a is interposed between the thermal head 61 and the platen roller 63 together with a recording paper (transfer body) 70 provided thereon a dye receiving resin layer 70a. The ink sheet 62 and the transfer body 70 are run together while they are pressed against the thermal head 61 by the rotating platen roller 63.
Upon heating the ink (transfer dye) in the ink layer 62a selectively by the thermal head 61, the ink is transferred to the dye receiving resin (receptor) layer 70a of the transfer body 70 to form dotted images thereon. Thermal transfer recording proceeds in this manner. In general, thermal transfer recording is effected in a line process in which a long thermal head is fixed perpendicular to the direction of running the recording paper.
However, a recording method of the type described above suffers the following disadvantages.
(1) The ink sheet which supplies the ink is disposed after using it only once. The used ink sheets hence heap as wastes and cast serious problems concerning energy conservation and environmental protection.
(2) There is also proposed a means of producing full-color images using the ink sheet for a plurality of times with an aim to reduce the wastes. However, concerning that the transfer dye layer and the transfer body are brought into contact with each other, if a transfer dye A is transferred to a transfer body and if another transfer dye B were to be transferred superposed on the previously transferred dye A, the transfer dye A on the transfer body would be transferred back to the layer of the transfer dye B on the ink sheet and thereby stain the layer of the transfer dye B. This signifies that a process of this type yields prints of poor quality if printing proceeds to a second sheet and further thereon after printing the first sheet.
(3) The ink sheet which occupies a large volume is a great obstacle for implementing a compact printer device.
(4) Image transfer in a so-called thermal transfer printing method is based on the thermal transfer phenomena of a dye. Accordingly, the image receiving layer must be heated sufficiently to diffuse the dye inside the image receiving layer of the image transfer body. This impairs the thermal efficiency of the process.
(5) To efficiently transfer the image, the ink sheet must be pressed against the transfer body by applying a high pressure. This inevitably requires a printer of high mechanical strength and poses a great hindrance in realizing a compact and light weight printer device.
(6) The sensitivity of image transfer can be improved by increasing the miscibility of the dye receiving resin and the image transfer dye. However, in general, a dye receiving resin that is highly miscible with the image transfer dye has poor preservation stability, and particularly, is inferior in light stability.
As described in the foregoing, a so-called thermal transfer method is subject to various problems. It has been therefore required to develop a technology for implementing a compact and light weight printer while reducing wastes and the consumption of transfer energy, yet making full use of the aforementioned advantages of the thermal transfer recording method.
In the light of the aforementioned circumstances, the present inventors have extensively conducted a study for implementing a thermal recording method which meets to the present demand. As a result, the present inventors have successfully developed a recording technique as illustrated in FIG. 34.
Referring to FIG. 34, minute interstice is provided between a recording unit having a thermally fusible dye layer and a recording body 50 having a dye receiving layer faced to the recording unit. Then, a liquefied dye 22 on the recording unit is vaporized selectively using a proper heating means such as a laser L, and is transferred through the interstice to form an image having a continuous gradation on the recording body 50. This procedure is repeated on each of the image signals obtained by separating the initial image signal into the three subtractive primaries, i.e., yellow, magenta, and cyan. In this manner, a full-color image having a continuous gradation can be obtained.
In this recording method, preferably, the recording body 50 is faced to the upper side of the recording unit so that the laser beam L might be focused in the vicinity of the upper face of a vaporizing portion 67. In this manner, the vaporized dye 32 can be moved upward. If this were to be effected in a reversed manner, i.e., if the laser beam were to be focused in the vicinity of the lower face of the vaporizing portion to allow the recording portion and the vaporized dye located in the lower side to move, the liquefied dye would generate a convection in the vaporizing portion to impair the thermal efficiency.
According to the method of the present invention, the dye which is consumed for the recording is almost free of a binder resin. Thus, the dye can be supplied continuously to the recording portion by flowing the dye from the dye reservoir in a fused state at a quantity corresponding exactly to the consumed amount, or by continuously applying the dye to a proper base which is transferred to the recording portion. The recording portion can be thus subjected to repeated use, and the problem (1) as mentioned in the foregoing can be overcome by principle in this manner.
In the method according to the present invention, the dye layer is not in direct contact with the recording body. Thus, the problem (2) of impairing the image due to back transfer of the recording dye previously transferred to the recording body to a layer of a differing dye can be solved. At the same time, the problem (3) of making the printer device light weight and compact can be coped with by thus eliminating the ink sheet and by using a small dye reservoir for supplying the dye.
The recording method according to the present invention comprises a recording mechanism based on the vaporization of the dye. Accordingly, it is not necessary to heat the image receiving layer nor for the ink sheet to be pressed against the transfer body by applying a high pressure. Thus, the problems (4) and (5) can also be solved. Moreover, the recording portion and the recording body are not brought into direct contact with each other. This fact, by principle, not only excludes thermal fusion from occurring between the recording portion and the recording body, but also makes recording possible even when a dye less miscible with the resin in the image receiving layer is used. Thus, the dye and the resin for use in the receiving layer can be designed more freely and can be selected from a wider variety of materials to solve the problem (6).
With further investigation, however, it was found that the recording portion shown in FIG. 34 had yet the following problems to be overcome.
The laser beam is focused through a glass sheet 14 to generate heat. Thus, even when a dye containing an infrared absorbent is used, the dye in the vaporizing region must be confined to a thickness of several micrometers to generate the vapor of the dye. The fusible dye cannot be smoothly supplied to such a thinly confined region.
Moreover, if bumping occurs on the liquefied dye, not only a favorable recording is obtained, but also a cavity 68 illustrated with a virtual line in FIG. 34 forms due to the bumping. Because the liquefied dye cannot be replenished immediately due to its high viscosity, a defective portion results in the recorded image due to the cavity 68.